Adjustable mounted, reciprocating doctor device including blade and air blast means



Sept. 15,-1964 M. M. BRUNDIGE 3,149,005

ADJUSTABLY MOUNTED, RECIPROCATING DOCTOR DEVICE INCLUDING BLADE AND AIR BLAST MEANS Filed Jan. 6, 1960 6 Sheets-Sheet 1 no i no f Q Q N I a & o o

M I W. o

K) 2 I o I Q a ,N WM 9 lhl' 0 INVENTOR MAURICE M. BRUNDIGE BY iv/ha? 6w ATTORNEYS.

Sept. 15, 1964 M. M. BRUNDIGE ADJUSTABLY MOUNTED, RECIPROCATING DOCTOR DEVICE INCLUDING BLADE AND AIR BLAST MEANS 6 Sheets-Sheet 3 Filed Jan. 6, 1960 INVENTOR MAURICE M. BRUNDIGE A TORNEYS.

Sept. 15, 1964 M. M. BRUNDIGE 3,149,005

ADJU-STABLY MOUNTED, RECIPROCATING DOCTOR DEVICE INCLUDING BLADE AND AIR BLAST MEANS Filed Jan. 6, 1960 6 Sheets-Sheet 4 FIG. 4. [P

INVENTOR MAURICE M. BRUNDIGE AT ORNEYS.

\ 3,149,005 DEVICE Sept. 15, 1964 M. M.IBRUNDIGE ADJUSTABLY MOUNTED, RECIPROCATING DOCTOR INCLUDING BLADE AND AIR BLAST MEANS 6 Sheets-Sheet 5 Filed Jan. 6,1960

INVENTOR MAURICE- M. BRUNDIGE N A II I p main B jom ozzu Homo. Essmmwm uumou B3. 0 8.2: o o 22: 0

A TORNEYS.

Sept. 15, 1964 Filed .Jan. 6, 1960 M. M. BRUNDIGE ADJUSTABLY MOUNTED, RECIPROCATING DOCTOR DEVICE INCLUDING BLADE AND AIR BLAST MEANS 6 Sheets-Sheet 6 COAT WEIGHT LBS. PER 3300 59; FT.

MAURICE M. BRUNDIGE BY rawa,?- uwg AT ORNEYS.

BLADE PRESSURE NORMAL FORCE'IN P.S.l.

United States Patent 3,149,005 ADJUSTABLY MOUNTED, RECIPROCATING DOC- TOR DEVICE INCLUDING BLADE AND AIR BLAST MEANS Maurice M. Brundige, Westernport, Md., assignor to West Virginia Puip and Paper Company, New York, N.Y., a corporation of Delaware Filed Jan. 6, 1960, Ser. No. 788 16 Claims. (Cl. 118-79) This invention relates to coaters for web material and more particularly to coaters of the type that may be described as inverted blade coaters. In coaters of the type referred to, a web travels first past a coating station at which the applicator applies coating material to one 3,149,0d5 Patented Sept. 15, 1964 7 gap may therefore be directly controlled by the pressure face of the web, and the web is thence carried forward upon a backing roller past a doctoring station, at which station a doctor blade bears against the coating on the web and serves to spread the applied coating evenly, and to squeeze back or scrape away surplus coating, thereby to render the retained coating of a more nearly uniform, prescribed weight.

A primary object of the invention is to provide an improved means for controlling the blade pressure against the coated paper whereby coatings ranging from minimum weight to weights considerably in excess of the highest weights heretofore successfully applied by conventional trailing blade coaters, can be uniformly and dependably controlled.

In any trailing blade coating system, the shearing of a high viscosity suspension in the wedge shaped gap between the blade and the web, produces a pressure which tends to push the blade away from the paper, or compresses the paper, or does both. The force exerted upon the blade by external means pushes the blade toward the paper until the gap at the exit side of the blade is so adjusted that, in relation to the speed, the average viscosity of the coating, and the length of the gap, the pressure de-- veloped by the coating is just enough to counterbalance the externally applied force.

In the more popular, conventional trailing blade coaters the blade is generally very thin and is made to approach the backing roller at an angle of from 45 to 60 with the plane tangent to the backing roller at the line of blade contact, the gap being provided between a small lip of the blade which is caused to bend toward the direction of motion of the web and the roller. This arrangement produces difiiculties because of contradictory demands. In order for the lip to bend substantially it has to be thin, but a thin lip tends to be too flexible in the direction of the axis of the backing roller, i.e., in the cross machine direction. This flexibility allows thick and thin streaks and waviness in the cross direction of the paper. To avoid this the blade is pressed hard against the backing roller,'a necessity which compels a low coating weight. In other words, uniformity of coating weight in the cross direction demands high pressures on a thin lip, and this in turn demands low coating weights. If the lip of the blade is made thick to stabilize it, it will bend only under excessively high pressures, because the stitfness of the lip increases in more than linear relation to the thickness of the lip. With the usual, unyielding mounting for the blade the thick blade is quite unsatisfactory.

In accordance with the present invention a comparatively thick blade is employed, but instead of depending upon bending of the blade to control pressure and coating weight, the whole combination of blade and blade holder is mounted for movement about a fulcrum axis parallel to the axis of the backing roller, and means is provided for urging the entire lever system under controlled, yielding pressure in a direction to urge the blade obliquely toward the backing roller. The average width of the exerted on the blade and blade holder combination, instead of by mere deformation of the blade lip. A more uniform gap width is thus obtained both in the machine direction and in the cross machine direction. The gap width is more readily controlled at wider gaps, since it is directly related to pressures which are under the control of the operator, and the yieldable pressure means can be forced back momentarily to clear an obstruction without materially increasing the pressure. 11 the previous systems the gap width has depended upon the uniformity of curvature and the length of the bent lip, neither of which was under the control of the operator. The present system does not, however, demand the use of a completely rigid blade, being thoroughly compatible with the use of a blade which has a substantial degree of flexibility and which therefore makes reasonable provision for local variations of fiexure.

It is a further feature that means is provided for regulating over a wide range the pressure yieldingly applied to the blade holder, and this even during operation of the coater. Without stopping the coater, pressure adjustment can be made to compensate for blade wear, and particularly to compensate for operating variables resulting from blade wear, such as blade width, blade stiffness, blade angle, and the bearing area of the blade lip against the coated web.

In inverted blade coaters, the fact that the coating ma terial is first applied as a coating by an applicator and then doctored, makes the association of end dams with the backing roller unnecessary. It has nevertheless been the practice in the past to confine the application of the coating to an area which is spaced inward from the edges of the web. As a consequence the web has included marginal areas which receive no coating, or marginal areas which receive some coating, but in variable and unsatisfactory amounts. The uncoated and defectively coated Web margins make the web awkward to feed and to reel, and require the trimming away of these margins at the sides of the web. It is a further important object of the present invention to obviate these coating imperfections, and thereby to do away with the necessity for removing uncoated portions or defectively coated portions of the Web by edge trimming.

In accordance with the invention the applicator is made wide enough to coat the entire width of the web, and, if desired, to coat the exposed margins of the backing roller to the very ends of the roller. By this means the web is coated throughout its entire width, and part or all of the exposed end or marginal portions of the roller circumthe doctor blade alone serves adequately to limit the material carried past the doctor blade on the exposed roller margins, and to prevent the accumulation of dried out deposits on the roller.

With heavy material, such as paperboard, there is a tendency for a portion of the coating material deposited on the exposed roller margins to adhere to the side edges of the web and to work under the side margins of the web, because of the comparatively wide spacing of the ends of the doctor blade from the backing roller. It is a feature that air jets are provided for blowing air backward between the blade edge and the margins of the backing roller beyond the side edges of the web, for limiting markedly the amount of coating material which can pass the doctor blade and to prevent excess coating from adher-ing to the edges of the web and Working under the Web due to film split when the web parts with the backing roller.

Other objects and advantages will hereinafter appear;

In the drawing forming part of this specification,

FIG. 1 is a fragmentary perspective View of an illustrative coater which embodies features of the invent-ion;

FIG. 2 is a fragmentary plan view, broken away intermediate its ends for compactness of illustration, showing the coater of FIG. 1;

FIG. 3 is a fragmentary View in side elevation, partly broken away, of the coater of FIGS. 1 and 2, the view being taken on 'a larger scale than FIGS. 1 and 2;

FIG. 4 is a sectional view taken upon the line 4-4 of FIG. 3, looking in the direction of the arrows;

FIG. 5 is a sectional detail view taken on the line 5-5 of FIG. 2, looking in the direction of the arrows, the view being upon a larger scale than any of the preceding figures;

FIG. 5A is a sectional view showing an unbacked semirigid blade in the holder, the blade being about twice as thick as the blade of FIG. 5;

FIG. 6 is a diagram illustrating the transformations of forces which occur in two illustrative examples; and

FIG. 7 is a series of graphs which show the effect that blade thickness has on the relationship of coat weight to blade pressure.

The coater comprises identical side frame members 10 and 12, the frame member 12 being omitted from the showing of PEG. 1. The frame members It) and 12 either directly or indirectly support all of the mechanism described herein. The coater comprises a constantly driven backing roller 14, whose shaft 16 is rotatively supported through bearings 18 by the frame members 10 and 12.

A supply of coating material is maintained in a pan 2%. A pickup or feed roller 22, rotatively carried by the frame members Hi and 12, runs in the pan 2% and serves to pick up the coating material 24 and to apply it to a paper web P which travels in a counterclockwise direction, as viewed in FIGS. 1 and 3, around an extensive arc of the backing roller 14.

It is an important point that the roller 22 is wider than the paper web, the roller 22 being desirably equal in length to the backing roller 14, so that it applies the coating not only to the paper web but to the margins of the roller 14 right out to the ends of the roller. This is a feature of importance in connection with the full width coating of the web. By having the coating applied beyond the side boundaries of the web the application of an even coating right out to the web edges is assured, and as a consequence the coated paper is adapted to be fed without difiiculty in the machine and to be reeled in a smooth and even manner. Because there is no unevenly coated margin to impair the quality of 'the product and to interfere with smooth handling and reeling, the need for trimming and the waste which trimming entails, are avoided.

The practicability of rull width coating depends upon the absence of end dams and upon the manner in which the paper web and the backing roller 14 are doctored, as

will be explained.

After passing the station at which the coating is applied to the paper by the applicator roller 22, the paper web P travels past a doctoring station at which a doctor blade 26 acts upon the coated web and upon the margins of the backing roller 14 to even out the coating and to limit the amount which passes the doctor blade to a predetermined substantially even thickness.

The doctor blade 26, as best seen in PEG. 5, is held, together with a backing bar 23, in a rigid holder 30, the blade, backing bar and holder having the conventional construction of the well-known Lodding doctor. The blade 26, made of spring steel, has studs 32 applied through its margin remote from the backing roller 14, which studs project from opposite faces of the blade. Each stud at the upper side, as seen in FIG. 5, fits snugly through a hole formed in the backing bar 28, the studs serving to control the relative positions of the blade 26 and the bar 28. Prebeveled blades are desirably used.

The holder 30 includes spaced upper and lower members 39 and 35. The member 36 is formed with a channel just wide enough to receive the lower portions of the studs 32 comfortably, while the members 39 and 36 are so spaced from one another that the studs are confined betwen the members with little capacity for free play of the blade and backing bar. The blade 26 and the backing bar 28 are just long enough to extend from a stop finger 38 at one end of the holder to a removable retaining pin 4%) at the other end of the holder, finger 38 and pin 40 being shown on FIG. 1.

The blade 26 and the backing bar 28 are made longer than the roller 14 so that they may be oscillated axially of the roller and still extend at all times to or beyond the ends of the roller 14. When the blade 26 becomes worn and requires to be replaced, the retaining pin 40 is temporarily removed, and the blade 26 and the backing bar 23 are drawn lengthwise from Within the holder 30.

.When the blade and bar have been withdrawn, the bar may be readily lifted off of the blade and associated with a fresh blade for reinsertion in the holder 30. These details do not form features of the present invention since they conform to the characteristics of the conventional Lodding doctor blade assembly.

The holder 30 is fixedly mounted upon a carrier 42 which includes a cylinder 44 and an angle bracket 46. The holder 30 is secured to the angle bracket by a series of screws 48. The cylinder 44 is keyed to a shaft 50 which is adapted to be rocked to and fro for carrying the doctor blade assembly away from and toward the backing roller 14.

The shaft 56 is rotatively supported in bearings 52, the V bearings, in turn, being mounted on angular bearing brackets 54 as shown in FIG. 4. Each bracket 54 includes a platform portion 56 and a vertical portion 58. Each bracket portion 58 is formed with slots, through which bracket clamping lag screws 60 are passed freely, the;

screws being threaded into the respective frame members It and 12. The brackets 54 may be adjusted toward and from the backing roller 14 for changing the distance between the axes of the roller 14- and the shaft 50, and consequentially adjusting the angular disposition which the blade 26 and the blade carrier 45 will assume about the axis c of shaft 50 when urged toward the backing roller by a rocking movement applied to the shaft.

The brackets 54 also carry bearings 62 in which a shaft 64 is rockably mounted. The shaft 64 has affixed to it an angle bar 66, upon which a pair of bent arms 68, bifurcated at their lower ends, are adjustably and removably secured by set screws as shown in FIG. 3. Each arm 68 includes an upwardly extending supporting arm 72, an intermediate arm 74 which extends over the cylinder 44 and toward the roller 14, and an upstanding terminal arm '76.

Pairs of U-clamps 7S adjustably secure air jet tubes to the respective arms 76, the threaded legs of each U- clamp being passed through the associated arm 76 and having clamping nuts 82. threaded upon them. Each air jet tube 80 is tapered at one end in the machine direction and broadened in the cross-machine direction, and is adapted to have the tip located just outside an edge of the paper Web and in close proximity to the slot formed between the roller 14 and the edge of the blade 26. Each illustrative jet measures internally at its tip three-quarters of an inch by .012 inch, and desirably utilizes an air pressure of about eighty pounds per square inch. Arms 84, fixed on the cylinder 44, extend upward into bearing engagement with the arms '74, normally determining the relation of the tubes 80 to the roller 14 and the blade 26, and serving, when the cylinder 44 is turned clockwise (as viewed in FIG. 3) to swing the blade 26 away from the roller 14, and to swing the tubes 80 back out of the way also.

. Provision is desirably made for oscillating the blade 26 lengthwise of the roller 14-, although this is not an essential feature of the invention. At one end of the shaft beyond the frame member 12, the shaft has fast upon it a pair of spaced, confronting discs 86 as shown in FIG. 2. An electric motor 88, having unitary with it a speed reducing gear box 90, is mounted upon an extension bracket 92 of the frame member 12. An output shaft 94 of the gear box has eccentrically fixed upon it a roller carrier 96. The roller carrier 96 is formed with a reduced cylindrical bearing portion, also eccentric with relation to the shaft 94, upon which a roller 98 is rotatably mounted. The roller 98 fits snugly between the discs 86, and acts through the discs to impart one complete oscillation to the shaft 50 for each complete revolution of the shaft 94. The oscillation of the shaft 51) is transmitted to the blade 26 through the cylinder 44, the bracket 46 and the holder 30.

It is a primary freature of the invention that the blade 26 is normally pressed yieldingly and with regulated pressure against the roller 14. To this end, the shaft 50 has keyed upon it, at each of its ends, two parallel crank arms 130 which are connected to one another by a crank pin 102 as shown in FIGS. 1 and 3. The crank arms 130 oscillate with the shaft 50.

Force for turning the crank arms clockwise or counterclockwise is transmitted by piston rods 1194 from pistons 106 in air cylinders 168. Each piston rod 1114- includes at its forward end a cross sleeve 110 through which the associated crank pin 192 extends with freedom for rocking movement. Each cross sleeve 110 is considerably shorter than the space between the associated crank arms 1110. The lost motion between the cross sleeves 110 and the cranks 106 permits the cranks to oscillate with the shaft, without afiecting the cross sleeves. The pairs of crank arms 100 are disposed, respectively, within angular recesses 112 of the frame members 19 and 12. The left ends of the air cylinders 168 are supported from the crank pins 162 through the piston rods 104.

The right end of each air cylinder 108 is pivotally sup ported from, and within, a frame extension composed of upper and lower angle plates 114 and 116 and a transverse end plate 118. Each cylinder 108 includes at its right end two parallel ears 120 and 122 which are connected to one another through a cross pin 124. A screweye 126 which consists of a cross sleeve 128 and a threaded stem 130, has its stem passed through the plate 118 and fixed in place by nuts 132 and 134, the nuts being threaded on the stem at opposite sides of the plate 118 to clamp the plate 118 firmly between them. The sleeve portion 128 of the screw-eye 126 receives the cross-pin 124 and supports the pin with freedom for rocking movement.

Normally, air under regulated, constant pressure 1s maintained in the left end of each cylinder 108 for urging the shaft 51 counterclockwise and thereby pressing the doctor blade 26 against the backing roller 14, the right end of each cylinder being at the same time open to the atmosphere. The connections to the opposite ends of the air cylinder may be reversed at will, however, for swinging the blade 26, the blade holder 30, and the air jet tubes 80 away from the backing roller 14 when required for cleaning, threading, etc.

Gravity loading of the doctor blade assembly amounts to the equivalent of a substantial air pressure per square inch in the left hand ends of the cylinders. If, under special circumstances, the gravity loading exceeds the operating pressure desired, air pressure may be switched to the right ends of the cylinders and regulated to counterbalance any desired fraction of the gravity loading. The gravity loading can be nullified by an air pressure of about twenty pounds per square inch in the right hand ends of the cylinders.

A common air conduit 136, having its intake end connected to a source of air under pressure (not shown), is equipped with a manually adjustable pressure regulating valve 138 for maintaining the air to the cylinders under any desired constant pressure. The conduit 136 delivers to branch conduits 140 which lead to the respective cylinders 108. Each branch conduit is provided with a valve 142, and each valve has an operating arm 144. As shown in FIG. 3, valve 142 is in position to place the left end of a cylinder 108 in communication with the conduit 136 through a secondary branch conduit 146 and the right end of the cylinder in communication with the atmosphere through a secondary branch conduit 148. There are necessarily two of the valves 142, one for each cylinder 108, the valves being arranged for simultaneous operation by means not shown. The valve operating arms 144 may be mechanically connected to one another, but preferably they are arranged to be spring biased to the condition illustrated in FIG. 3, and to be simultaneously andinstantaneously operated to the reverse position illustrated in broken lines in FIG. 3 by solenoids (not shown) which are controlled by a common electrical switch in a common electrical circuit (not shown).

It is not requisite that the blade 26 be backed as shown in FIG. 5, and in fact there are advantages in using a thicker unbacked blade 26a as shown in FIG. 5A. The blade flexures of a thin, backed blade such as blade 26 in FIG. 5, can, through suitable backing, be limited to make them equal to the fiexures of the thicker unbacked blade under corresponding total radial pressures, but the thicker blade is generally to be preferred. This is true chiefly because a total given radial or normal pressure is transmitted through a larger bevelled face when the thicker, unbacked blade is used, and therefore applies a smaller pressure in pounds per square inch for a given cylinder loading. This produces a higher coating weight for the same total radial pressure or, conversely expressed, requires a higher total radial pressure for the same coating weight. The blade and backing bar are not required to be freely separable from one another as in FIGS. 1 to 5, but may be united in various'ways as by an epoxy resin cement.

The effects of a number of variables have been carefully investigated, in each instance by varying the factor under investigation while stabilizing or balancing out other factors, which, if not controlled, would mislead.

One such investigation has had to do with variations of the angle made by the blade with the plane tangent to the backing roller at the line of blade contact. As the blade angle is diminished the wedging outward of the blade by the traveling coating material is favored, and this is desirable so long as control is not impaired. Control is greatly impaired as the blade approaches tangency. Tests run with a blade angle as low as 25 have worked out very satisfactorily. Control is also impaired as this blade angle is increased toward a right angle. Tests run with a blade angle of 50 have worked out quite satisfactorily. Exact limits have not been determined.

Within limits, the chief importance of the blade angle is the effect which it has upon the ratio of total force ap plied along the arc of blade travel to the total derived or resultant force in a direction radial to the backing roller 14.

This transformation of forces is, in itself, important, however, because it provides a means of selecting the output-input force ratio. A relatively low output-input ratio is to be preferred because this calls for a comparatively high, and hence wide, range of input pressures so that relatively fine gradations of radial or normal pressure can be realized. With a high input pressure, moreover, the apparatus is less responsive to disturbing influences such as shaft and piston friction, and possible deviations of air pressure from the exact value for which the control valve is set.

It will be observed that the active edge of the blade 26 is carried toward the roller 14 along a selected are (see a t and a t (FIG. 6) for two examples) whose center coincides with the axis of the shaft 50. The are referred to meets the circumference of the roller 14 at an acute angle, the active blade edge when in the operative position illustrated in FIG. 3 being located only a short ii distance above the common axial plane cc of the roller 14 and the shaft 59.

The blade and blade holder assembly extends upward and to the left (FIG. 3) across the line of centers -0 and this disposition favors the wedging action of the coating relative to the blade, because it makes the angle formed by the blade and the plane tangent to the periphery of the roller 14 at the line of contact decidedly more acute than it would be if the blade tip extended radially from the axis c of the roller 50. The angle is made still more acute by the slight fiexure of the blade.

As shown in FIG. 6, the radius of the backing roller 14 is taken as eight inches and the line of centers c-c is taken as 17% inches. These dimensions are consistent with those of actual equipment embodying the invention.

According to a first example the distance from the axis 0 to the blade edge is 9 inches, causing the blade edge to engage the roller 14 along an element t of the roller. A single unit of force applied at right angles to cm along the line of a t; and represented in magnitude by the length o t can be analyzed as having a component parallel to c t and proportional in magnitude to 0 x and a component in alignment with radius ct; and proportional in magnitude to x 1, or 3.06 units of force. The ratio of 1 to 3.06 is the ratio of total force applied in the direction perpendicular to c t to the total force derived in the direction of the radius ct According to a second example the distance from the axis c to the blade edge is 10% inches, causing the blade edge to engage the roller 14- along an element of the roller. A single unit of force applied at right angles to c t along the line ogtg and represented in magnitude by the length 0 2 can be analyzed as having a component parallel to c t and proportional in magnitude to 0 x and a component in alignment with radius ct and proportional in magnitude tox t or 1.83 units of force. In this case the ratio of l to 1.83 is the ratio of the total force applied perpendicular to c 2 to the total force derived in the direction of the radius ct It is evident from these examples that the ratio of applied force to derived, radial or normal force, is increased as the line of contact of the blade with the roller 14 is shifted upward through the employment of wider blades and/or the shifting of the axis c nearer to the axis 0.

The utilization of a high ratio of applied force to the derived radial force is considered advantageous because the need for a high applied force affords a higher and wider range of cylinder pressure adjustment for a given range of total derived pressure, and this makes possible a finer control. This advantage is enhanced by the fact that deviations of operation caused by piston and shaft friction are relatively minor when the total cylinder pressure is high.

As has been noted, it is not the total derived pressure alone which determines the Weight of the coating, but rather the normal pressure per square inch of effective blade surface. This figure is obtained by dividing the total normal pressure by the area of the beveled face of the blade. Doubling the blade thickness for a given total pressure cuts the pressure per square inch in half. Put conversely, a specified pressure per square inch requires twice as much applied pressure for a thick blade as for a blade one-half as thick.

With identical blade angles for thick and thin blades, and with the Web running at one thousand feet per minute it was found that the coating weight increased substantially in inverse proportion to the logarithm of the pressure as the pressure was reduced. In each instance, as shown in FIG. 7, the negative slope of the curve (plotting the logarithms of pressures as abscissae and coat Weights as ordinates) remained constant to a certain point, then increased abruptly and thereafter remained constant at the increased value as the pressure continued to diminish.

The points at which the coat weight plots change slope r 8 abruptly occur at somewhat higher coat weights and lower pressures (expressed in pounds per square inch) for the thicker blades. The values of the normal force for the point of change were about 325 p.s.i., 225 p.s.i. and 125 p.s.i. for the backed .012" blade, the backed .015 blade and the unbacked .031" blade, respectively. The slopes of the plots were steeper for the thicker blades. The coat weights at the break points were 3.75 pounds, 4.5 pounds and 5 pounds, respectively, for the .012", the .015" and the .031" blade.

For the .012 blade the coat weight varied from 3.5 pounds at 440 p.s.i. to 6.75 pounds at 150 p.s.i. For the .015" blade the coat weight varied from 2.75 pounds at 470 p.s.i. to 14.25 pounds at 62.5 p.s.i. For the .031" blade the coat weight varied from 3.88 pounds at 230 p.s.i. to 12 pounds at 82.5 p.s.i.

The break in the curve is believed to occur at the point where the direct support of the blade by the fibers becomes negligible, and the blade actually begins to be supported in spaced relation to the fibers by the coating material.

The total results indicate that high coat weights can be obtained with a .015" blade at the one thousand foot speed range, but that in the five hundred foot speed range a thicker blade is required. With the unbacked .031" blade the slope was found to be relatively steep and coating materials of lower solids content and/or lower viscosity than those employed in the tests may be desirable for reducing the steepness of the slope and thereby obtaining better control. With a thin blade, it is dilficult to obtain low pounds per square inch values because of the extremely small area of blade contact. The indication is that the blade thickness aliects the coat weight for a given speed and normal pressure in pounds per square inch, that is, above the coat Weight pressure necessary to satisfy base coat roughness.

The results of tests indicate that in order to obtain coat weight control over a wide range, the blade must be sufiiciently rigid, through its inherent stiffness and/ or through backing bar support, to permit only minor flexing at the tip. In one test employing a more flexible blade the coat weight was increased from five to twenty-four pounds by increasing the air pressure in the left ends of the cylinders from 60 p.s.i. to p.s.i., but there was no control at the higher pressure because the blade was flexed to an essentially tangent condition to the roller at the point of contact.

In all runs in which the blade was prevented from large angle flexing, by limitation to the range of about 5 to 10, the coating weight was uniform across the web and all grit and other detritus was passed without extensive streaking. When streaks did occur they moved back and forth with the doctor blade and soon disappeared. Oscillation of the blade presented no problem. The ready passage of grit is credited, in part at least, to the low angle made by the blade tip with the tangent plane at the line of contact. Doctor blade oscillation may be entitled to some of the credit, but this has not been definitely established. The angular bending limits stated above could undoubtedly be extended through adjustments which appropriately increase or diminish the angular relation of the rigid blade holder to the tangent plane at the line of blade contact.

It was established by tests that the weight of the coating does not change appreciably as the paper gains speed from f:t./rnin. to 500 ft./min. but it that does show a substantial increase at one thousand feet per minute over that at one hundred or five hundred feet per minute. The fact that increasing the speed from one hundred to five hundred feet per minute does'not materially increase the coating weight is attributed to the higher absorption of liquid by the paper between the applicator station and the doctoring station at the lower speed as opposed to a limited increase of hydrodynamic etfect (increased shear strength of the coating) at the higher speed. The increased coating weight at one thousand feet per minute is clearly attributable to a substantially increased hydrodynamic eifect. The magnitude of the hydrodynamic effect increases with increase of speed. The influence of the hydrodynamic effect becomes more pronounced as (l) the viscosity or solids content of the coating material is increased; (2) the blade angle is diminished; and (3) the thickness of the blade is increased.

Viscosity and solid content of the coating material are important because the coating weight increases with increase of either of these factors. Viscosity and solids content are also important because they may be adjusted up or down to control the pressure-coat-weight curve, and thereby assure controllable conditions for coatings under normal pressures which involve more than usual difficulty.

The total pressure applied by the blade to the backing roller for any chosen angular relationship is controlled and limited for any given set-up by the measure of the air pressure maintained in the cylinders and the gravity loading of the blade. The coat weight can be chosen and controlled as desired by adjusting the air pressure in the cylinders.

This is an extremely important feature, not only for accommodating the mechanism to the production of a desired, controlled coating Weight with the material chosen and under the em'sting conditions of blade angle and thickness, web speed, etc., but for effecting compensation for changes of condition during operation.

As the blade wears in use, a number of changes occur which tend progressively to affect the weight of the coating. Wearing away of the blade shortens the distance of the blade edge from the axis c and thus permits the blade to drop down so that the angle formed between the blade and the roller surface is increased. Because of the change of blade angle which results from blade wear, the area of the beveled face of the blade is diminished progressively, and hence the pressure per unit area is progressively increased.

All of the variables referred to, and others can be compensated for without interrupting the operation of the coater, merely by testing the actual coating weight produced from time to time and effecting appropriate adjustment of the setting of the regulator 138 to alter the air pressure of the cylinders 1&8.

The total pressure applied by the blade to the roller for any chosen angular relationship is limited by the measure of the air pressure maintained in the cylinder 198, plus the gravity loading of the blade. The total pressure is also maintained at a determined level, subject to progressive variation with wear as noted above, by the same means. The air loaded pistons also assure a cushioned application of the pressure.

In referring herein to blades employed as being semirigid, reference is had to blades which are considerably stiffer than unbacked blades of .012 inch thickness commonly employed, yet thin and flexible enough to yield locally to a practical degree in the cross-machine direction. By way of example only, an unbacked blade 3 inches wide by .031 inch thick meets this requirement very satisfactorily, while suitably backed blades .012 inch thick to something less than .031 inch thick, but hacked to have local fiexure not substantially greater than that of the .031 inch blade are also regarded as semi-rigid and are serviceable. It is not intended here to assert or imply, however, that blades having greater or less stiffness than unbacked .031 inch blades are without utility in the present apparatus.

In connection with the feature of applying the coating out to and beyond the web edges, it has been found that for papers of ordinary thicknesses, say up to .009 inch, or more the doctor blade alone is generally adequate for limiting the quantity of coating material carried past the blade on the margins of the roller 14. For papers of greater thickness and especially for paperboard, however,

10 the air jets .are found to be extremely useful since they serve to prevent the working of the coating material underneath the edges of the paper or paperboard. The jets are desirably made wide enough to sweep the coated margins of the roller immediately beyond the web edges. Where a hard surfaced backing roller is employed, a roller cleaning doctor blade (not shown), together with auxiliary devices (not shown), may be employed in the arc of the roller upon whichthe web does not run. The function of such auxiliary cleaning mechanism would be twofold:

(1) to make sure that the margins of the roller reach the appliactor in a clean condition at all times; and

(2) to eliminate any spots of coatings which may have been formed on the roller in the web carrying Zones. Such spots, if allowed to remain, will bulge thepaper outward and cause a serious deficiency of coating to occur in the bulged area.

Several different backing rollers have been successfully employed with this coater. I have used a rubber backing roller having a hardness of P & J 55, A5" ball, andI have also used a hard engraved copper plated steel backing roller, the engraving being 84 lines per inch. Any roller of intermediate hardness with a suitable surface finish may be employed.

While a certain preferred embodiment of the invention has been illustrated and described in detail, it is to be understood that changes may be made therein and the invention embodied in other structures. It is not, therefore, the intention to limit the patent to the specific construction illustrated, but to cover the invention broadly in whatever form its principle may be utilized.

I claim:

1. A coater for paper webs comprising, in combination, a substantially unyielding web backing roller on which webs of various widths less than the length of the roller may be caused to travel, means for applying coating ma terial to the roller carried web and to marginal portions of the roller itself beyond the web edges at an applicator station, a flexible spreading and evening doctor blade opposed =to the backing roller at a smoothing station, said blade being long enough to act upon the coating material previously applied to the web and to the coated roller margins beyond the side edges of the Web, and air jets located at the smoothing station and disposed to blow air directly against the coated roller margins and backward through the spaces between the coated margins of the Web backing roller and the opposed doctor blade at the web edges, for opposing the carrying forward of excess coating material on the roller margins and web edges and preventing coating from working under the web due to film splitting as the coated web leaves the backing roller.

2. A coater as set forth in claim 1 in which the blade is longer than the roller and means is provided for oscillating the blade axially of the roller.

3. A coater for paper webs comprising, in combination, a web backing roller of substantial hardness to maintain its normal shape at all points of the periphery of the roller when said roller is opposed to a doctoring device, said roller providing a backing on which webs of various widths less than the length of the roller may be caused to travel, means for applying coating material to the roller carried web and to marginal portions of the roller itself beyond the web edges at an applicator station, a spreading and evening doctor blade opposed to the backing roller at a doctoring station, said blade being long enough to act upon the coating material previously applied to the web and to the coated roller margins beyond the side edges of the web, and air jets located at the doctoring station and disposed to blow air backward through the spaces between the coated roller margins and the opposed doctor blade edges for opposing the carrying forward of coating material on the roller margins and preventing coating from working under the Web due to film splitting as the coated web leaves the backing roller,

a blade carrier supporting said blade, the blade carrier and the jets being mounted for swinging movement toward and from the backing roller, pneumatic power means settable to urge the blade carried yieldingly toward the backing roller or to swing it away from the backing roller, and means causing the jets to be swung away from the backing roller as an incident of the swinging of the blade carrier away from the backing roller.

7 4. A coater for paper webs comprising, in combination, a web backing roller of substantial hardness to maintain its normal shape at all points of the periphery of the roller when said roller is opposed to a doctoring device, said roller providing a backing on which webs of various widths less than the length of the roller may be caused to travel, means for applying coating material to the roller carried web and to marginal portions of the roller itself beyond the web edges at an applicator station, a spreading and evening doctor blade opposed to the backing roller at a doctoring station, said blade being long enough to act upon the coating material previously applied to the web and to the coated roller margins beyond the side edges of the Web, and air jets located at the doctoring station and disposed to blow air backward through the spaces between the coated roller margins and the opposed doctor blade edges for opposing the carrying forward of coating material on the roller margins and preventing coating from working under the web due to film splitting as the coated web leaves the backing roller, a blade carrier supporting said blade, the blade carrier and the jets being mounted for swinging movement toward and from the backing roller, pneumatic power means settable to urge the blade carrier yieldingly toward the backing roller or to swing it away from the backing roller, the jets being manually swingable away from the backing roller, and means including the blade carrier for limiting approach of the jets toward the backing roller and for causing the jets, when located in proximity to the backing roller, to be swung away from the backing roller as an incident of the swinging of the blade carrier away from the backing roller.

5. An inverted blade water for paper webs comprising, in combination, a rigid web backing roller of substantial hardness to maintain its normal shape at all points of the periphery of the roller when said roller is opposed to a doctoring device, said roller providing a backing on which a paper web may be caused to travel, an applicator roller opposed to said backing roller for applying coating material unrestrictedly to the roller backed web at an applicator station, a spreading and evening doctor blade opposed to the backing roller at a smoothing station which follows the applicator station and is spaced a substantial distance from said applicator station, said blade being more yieldable than the backing roller and sufiiciently thin and flexible to substantially conform locally to irregularities of contour of the backing roller and extending in the direction of backing roller rotation angularly to the plane which is tangent to the backing roller at the point of blade contact therewith for riding on the coating material which is carried away from the applicator station by the web, to redistribute and smooth the coating and reduce it to a substantially even, predetermined thickness, a blade holder supporting said blade, supporting means mounting the blade holder with freedom for movement about a fixed pivotal axis parallel Y 12 to the axis of the backing roller, pneumatic pressure means connected to the supporting means for constantly urging said supporting means, said bladev holder, and said blade as a unit rotationally about said fixed pivotal axis to urge said blade against said backing roller and web, pressure regulating means associated with the pneumatic means for maintaining and limitingtne total force which the pneumatic means applies through the blade to the coating, bracket means carrying the supporting means and adjustable directly toward and away from the backing roller to thereby effect a change in blade angle, means for fixing the bracket means in different positions of bodily adjustment and at different distances from said backing roller, and means connected to the pneumatic means for reversing the direction of action of the pneumatic means to thereby swing the blade away from the backing roller.

6. An inverted blade coater for paper webs as set forth in claim 5 in which the pneumatic pressure means includes a plurality of pneumatic cylinders each having a piston connected at spaced points to the supporting means, and conduit means furnishing compressed air to the cylinders; and in which the means for reversing the direction of action of the pneumatic means includes valve means settable to select the cylinder ends to which compressed air will be admitted, so that gravity induced movement of said supporting means, said blade holder, and said blade as a unit rotationally about said fixed pivotal axis may be supplemented or counterbalanced in whole or in part.

7. An inverted blade coater for paper webs as set forth in claim 5 in which the backing roller is metal.

8. An inverted blade coater for paper webs as set forth in claim 7 in which the metal backing roller is a copper plated steel roller.

9. An inverted blade coater for paper as set forth in claim 5 which the blade, at the line of bearing engagement with the backing roller makes an angle of about 25 to 50 with the plane which is tangent to the backing roller along that line.

10. An inverted blade coater for paper as set forth in claim 9 in which the hardness of the backing roller is less than 56 P 8: J, as measured with a /8 inch ball.

References titted in the file of this patent UNITED STATES PATENTS 904,231 Schou Nov. 17, 1908 1,264,506 Hahn Apr. 30, 1918 1,302,352 French Apr. 29, 1919 1,780,694 Alger Nov. 4, 1930 1,793,082 Goss Feb. 17, 1931 1,993,055 Gerstenberg Mar. 5, 1935 2,058,369 Taylor Oct. 20, 1936 2,155,083 Drewsen Apr. 18, 1939 2,257,373 Fanselow Sept. 30, 1941 2,322,533 Mayer June 22, 1943 2,427,339 Ljungquist July 26, 1949 2,534,320 Taylor Dec. 19, 1950 2,566,811 Stevenson Sept. 4, 1951 3,080,847 Justus Mar. 12, 1963 FOREIGN PATENTS 328,826 Switzerland Mar. 31, 1958 785,105 Great Britain Oct. 23, 1957 (Duplicate of Swiss 328,826) 203,977 Australia June 25, 1959 

1. A COATER FOR PAPER WEBS COMPRISING, IN COMBINATION, A SUBSTANTIALLY UNYIELDING WEB BACKING ROLLER IN WHICH WEBS OF VARIOUS WIDTHS LESS THAN THE LENGTHS OF THE ROLLER MAY BE CAUSED TO TRAVEL, MEANS FOR APPLYING COATING MATERIAL TO THE ROLLER CARRIED WEB AND TO MARGINAL PORTIONS OF THE ROLLER ITSELF BEYOND THE WEB EDGES AT AN APPLICATOR STATION, A FLEXIBLE SPREADING AND EVENING DOCTOR BLADE OPPOSED TO THE BACKING ROLLER AT A SMOOTHING STATION, SAID BLADE BEING LONG ENOUGH TO ACT UPON THE COATING MATERIAL PREVIOUSLY APPLIED TO THE WEB AND TO THE COATED ROLLER MARGINS BEYOND THE SIDE EDGES OF THE W EB, AND AIR JETS LOCATED AT THE SMOOTHING STATION AND DISPOSED TO BLOW AIR DIRECTLY AGAINST THE COATED ROLLER MARGINS AND BACKWARD THROUGH THE SPACES BETWEEN THE COATED MARGINS OF THE WEB BACKING ROLLER AND THE OPPOSED DOCTOR BLADE AT THE WEB EDGES, FOR OPPOSING THE CARRYING FORWARD OF EX- 